a substituent, a cyclic hydrocarbon group which may have a substituent, or an aromatic group which may have a substitutent; n is 0, m is 1, R1 is hydrogen, and Y is an aromatic group with a substituent ##STR133## R2 and R3 each represent hydrogen, and Y and R1 may be bonded to form a ring, and R4 is an alkyl group having 1 to 4 carbon atoms.